1. Field of the Invention
The present invention relates to a waterproof-sheet type of roofing shingle, and more particularly, to such a roofing shingle which can prevent bulging of waterproofing material overlying on a concrete substrate even in a tropical climate region, such as Okinawa region.
2. Description of the Prior Art
A single-layer type of non-walkable exposed waterproof sheets is known in the art, which is installed on a roof in a step of waterproofing work during construction. Such a waterproof sheet, Gum Cool Cap Ex having a thickness of 3.5 mm which is manufactured by TAJIMA ROOFING Co., Ltd., is normally attached onto a concrete substrate, such as a concrete slab. In general, each of such waterproof sheets is formed in a strip having a width of one meter and a length of eight meters. Such strips are applicable to various types of roofs, such as a large-sized flat roof of a concrete or steel structure building and a sloped roof of a wooden building or the like. In this specification, the term reading “single-layer type” of “waterproof sheet” is intended to be a waterproof sheet which can be attached directly on a roof substrate such as concrete slab, so as to form a substantially single waterproof layer or a single sheet made of integrated waterproof layers.
However, such a non-walkable exposed waterproof sheet necessarily raises a problem involved in bulging of its surface, since it is applied on the concrete substrate in intimate contact therewith. Such a problem often happens particularly in a tropical region, such as Okinawa region. This is mainly because a quantity of vapor or steam generated from the concrete is accumulated or stored between the waterproof layer and the concrete substrate when the waterproof layer on the entire roof is subjected to intensive solar heat, and the pressure of vapor or steam beneath the waterproof layer causes the waterproof layer to be expanded or bulged. Such an expansion or bulging of waterproof layer degrades or deteriorates the waterproofing performance and appearance of roof, and therefore, an approach for overcoming this problem is required.